Climbing Everest Without Oxygen: Your Questions Answered

By some accident of nature, the summit of Mount Everest is just possible to reach with a pair of unassisted human lungs. But only just.

Very few climbers are up to this supreme physical challenge, and some have died attempting it.

It is such a fine line that in low-pressure weather the summit becomes impossible to reach without supplementary oxygen because there are even fewer oxygen molecules in each gasp of breath.

Here are answers to some of the most common questions we get about summiting Everest without Oxygen:

Can You Climb Mount Everest Without Oxygen?

You can climb Mount Everest without supplementary oxygen. But only just. Superb physical specimens of the strongest climbers in the world can only just achieve this feat. Most of the oxygen-free ascents are by Sherpas.

The use of supplementary oxygen on Mt. Everest is now commonplace. From 1990 to 2006, more than 95% of those summiting the mountain did so using supplementary oxygen at some point during their ascent (Source: PubMed). Therefore fewer than 5% of Everest summits are achieved without oxygen.

Why Climb Mount Everest with No Oxygen?

It is so hard to climb Mount Everest without oxygen that huge kudos is given to the few people that have acheived this feat – and this is why people attempt to climb Everest without using Oxygen. There’s a big incentive to become one of the elite few that have managed to do it.

If you did manage to climb Everest without supplementary Oxygen, you’d become one of a very small, elite group of 200 people, or 4.5% of summiteers.

Can You Breathe on the Summit? Why the Air is Thin on Everest

Most climbers are able to breathe on the summit of Everest without supplementary oxygen – but only just.

At sea level, the effective percentage of oxygen in air is 20.9 %. The rest is inert nitrogen. On the summit of Mount Everest, the effective percentage is only 6.9% (source That’s a tiny percentage of the precious gas that sustains human life, and that’s why the air is so thin on Everest’s summit.

When I stood on the summit of Mount Everest in October 1993 I was able to remove my cranky Russian leather oxygen mask and move around normally while breathing heavily in the near-gale of wind.

I remember thinking that climbing hard without oxygen would have been difficult. The air pressure was only one-third of that at sea level, so every lungful of that thin, cold air contained only one-third of the oxygen molecules necessary to life.

Graham Hoyland on the summit of Mount Everest.
Graham Hoyland on the summit of Mount Everest in October 1993. You can see my oxygen mask and the rubber bladder beneath it. I was able to stand and walk around without needing to replace the mask.

Do Most Climbers Need Oxygen to Climb Everest?

All climbers need oxygen to climb Mount Everest because we are an oxygen-breathing animal! We usually get the gas from the air around us. So it’s important to distinguish between “oxygen” – which you’re breathing right now – and “supplementary oxygen”.

Most Everest climbers need supplementary oxygen to climb Mount Everest because the air pressure is so low that only one-third of the usual number of oxygen molecules can fit into each lungful.

As I mentioned earlier, of the 4,000 or so climbers who have summited the mountain, only around 200 people have climbed the mountain without breathing extra oxygen: that’s around 4.5%.

Why Do You Need Oxygen Masks and Tanks on Everest?

You need oxygen masks and tanks on Everest to supply extra oxygen molecules to your lungs. There isn’t an oxygen pipeline alongside the route up Mount Everest (yet) so climbers have to carry the extra oxygen gas on their backs. For the gas to be compact enough it has to be pumped into a tank or cylinder under great pressure.

Otherwise, the climber would have to carry a gas bag about the size of a car. This pressurised oxygen has to be accurately metered from the cylinder through a regulator, then released in a mask next to the climber’s mouth and nose. If there wasn’t a mask the oxygen would be lost.

A row of oxygen cylinders

How Much Oxygen is Needed to Get to the Summit?

Mount Everest climbers need around five oxygen cylinders to climb to the summit and return. Here’s how this is calculated:

Cylinder Capacity = 4 litres

Pressure = 4,300 psi

Litres of oxygen per tank = 1,200 litres

Weight of empty cylinder = 2.2 kg

Weight of full cylinder = 3.8 kg

Therefore a climber using 5 tanks or cylinders uses approximately 6,000 litres of supplementary oxygen, which weighs about 19kg including the tank.

What does 6,000 litres look like? About the size of the inside of a car. A water tank 2 metres in diameter and 2.5 metres also contains about 6,000 litres. (Source:

The gas must be completely water-free, otherwise, ice crystals will block the gas passages. So it has to be carefully manufactured. Poisk still makes the most reliable oxygen cylinders, in an ex-military facility in Russia.

These cannot be transported by air so they are transported by ship to southern India, then trucked to Kathmandu. This is why each oxygen cylinder costs around $1000 (source:

How Long Does a Climber’s Oxygen Supply Usually Last?

An Everest climber’s oxygen supply for the summit push, from Camp 4 on the South Col to the summit and back, lasts between 12 and 18 hours.

The climber will use three oxygen cylinders and will hope to get about six hours out of each one, using a flow rate of around 3 litres a minute. The flow can vary between 0.5 to 6.0 litres per minute (source

Can You Survive on Everest Without Oxygen? What if You run Out?

If you have started using oxygen low on the mountain, say around Camp 2, or use very high flow rates, you become acclimatised to it and you are in severe danger if you run out of oxygen at very high altitude. You could lose consciousness within a few minutes and die.

Oxygen sets can and do fail high up on the mountain. It happened to me. A mask might break, a hose freeze up or a regulator fail. In the spring 2018 Everest season twenty five to thirty regulators failed in the Death Zone (source, and all the climbers equipped with these had to descend immediately (source New York Times).

Do Sherpas Use Oxygen on Mt Everest?

Most Sherpas do use oxygen on Mount Everest. They are generally carrying more weight than their clients: extra oxygen cylinders, fixed ropes and spare clothing. Therefore they need more supplementary oxygen.

Nga Temba, our head Sherpa on the summit wearing a blue jacket and an oxygen system. With him in red is Expedition Leader David Hempleman Adams, also on oxygen.
Here’s Nga Temba, our head Sherpa on the summit in 2011 wearing a blue jacket and an oxygen system. With him in red is Expedition Leader David Hempleman Adams, also on oxygen.

You might also be interested in the history of oxygen use on Everest – including how it was used on the first attempts to the present day.

About Graham Hoyland

Graham was the 15th Briton to Climb Mount Everest. He has spent over two years across nine expeditions to the mountain and is the author of Last Hours on Everest, the story of Mallory and Irvine's fatal ascent.